1. Field of the Invention
This invention relates to a process for preparing polymer-polyols, polymer-polyols obtained by the process and polyurethane foams using the polymer-polyols. More particularly, the invention relates to a process for preparing polymer-polyols by polymerizing ethylenically unsaturated monomers in polyols free of any polymerizable carbon-carbon double bond in the presence of alkyl-substituted tertiary amines, to the polymer-polyols obtained by the process. and to polyurethane foams which are obtained by reaction between the polymer-polyols and polyisocyanates in the presence of foaming agents. catalysts, foam stabilizers and other additives.
2. Description of the Related Art
Processes for preparing polymer-polyols by polymerizing ethylenically unsaturated monomers in polyols are known in the art. Polymer-polyols are generally poor in dispersion stability and high in viscosity. To solve this, it is known to use chain transfer agents. There have been proposed processes wherein alkyl mercaptans are used as the chain transfer agent to obtain polymer-polyols with a low viscosity (U.S. Pat. No. 3,953,393 and Japanese Laid-open Patent Application No. 01-221403).
However. the polymer-polyols obtained by these processes have the problem of offensive odor. Moreover, because the rapid rise of viscosity cannot be suppressed when the concentration of the polymer is increased, it is difficult to obtain polymer-polyols of practical value.
Further, there has also been proposed a process which makes use of the chain transfer agents including mercaptans, ketones, alcohols, aldehydes, halogen compounds, benzene derivatives and, particularly, isopropyl alcohol (Japanese Laid-open Patent Application No. 58-210917). However, this process has to use large amounts of isopropyl alcohol in order to reduce the viscosity of a highly concentrated polymer-polyol. This leads to the problem that a large amount of energy is required for removing, purifying or collecting the alcohol.
Japanese Laid-open Patent Applications Nos. 50-149778 and 51-17924 set forth the use of organic compounds having a polymerizable carbon-carbon double bond and terminal hydroxyl groups as a dispersion stabilizer, which are apparently different from the present invention. Alternatively, there has been proposed a process wherein amines such as morpholine are used as a reaction regulator (Japanese Laid-open Patent Application No. 63-146912). In this process, however, a macromer containing an unsaturated bond consisting of a fumarate group is used as a dispersion stabilizer. This is completely different from the present invention. Although the use of the macromer is effective in stabilizing particles, there arises a problem of increasing the viscosity of the polyol. If morpholine which is a secondary amine is used, it is not possible to obtain polymer-polyols having good reaction curability.